1. Field of the Invention
The present invention generally relates to an apparatus, system and method for determining influx of formation fluids into a well borehole. More particularly, the present invention relates to apparatus and methods for determining influx by measuring and comparing to a reference value the dielectric constant and/or conductivity of the fluid surrounding the drill string in the borehole. Accordingly, the present invention includes apparatus and methods for determining the dielectric constant and conductivity of the fluids in the borehole.
2. Description of the Background
The detection of the influx of external fluids such as oil, water or gas from a geological formation into a well borehole during the drilling of the borehole through the formation is very important in oil and gas well drilling operations. Early influx detection is critical to safety and the avoidance of blowouts. Information obtained from the early detection of the influx of external fluids may be used to improve drilling efficiency by allowing the operator to adjust the weight and composition of the drilling fluid to very closely balance the formation pressure In addition, the influx of external fluids from the geological formation may be used to evaluate the oil or gas bearing qualities of the formation being drilled.
Early influx detection methods employed evaluation of surface measurable characteristics, e.g., mud pit volume, return flow rate and stand pipe pressure, to estimate influx. L. D. Maus, et al describe these early surface techniques in an article entitled, "Instrumentation Requirements for Kick Detection in Deep Water" published in August, 1979, at pages 1029-34 of V. 31 of The Journal of Petroleum Technology. M. H. Westerheim described an improved method of determining influx using improved measurements of annulus flow. This method minimized false alarms due to heaving of offshore rigs See "Heave Compensated Kick and Loss Circulation Detector" presented at the 1979 Offshore Technology Conference and published at page 41 of the proceedings thereof. A good summary of conventional methods for determining influx or kick was presented by D. I. Wilkie, et al in an article entitled "Dome's Kick Tolerance Formula for Safe Beufort Sea Drilling", published in March 1981, at page 33 of Ocean Industry. Wilkie described methods for determining kick including the observation of pressure measurements at the casing seat, the inference of pore pressure from seismic information, the observation of mud cuttings and the measurement of formation pressure.
The above references disclose surface measured or determined values to infer influx or kick Accordingly, these systems suffer from the significant time delays which might result between the time that influx or kick occurs at the drill bit and the drilling fluid is returned to the surface for examination. These delays not only may be disadvantageous but might also lead to undesirable blowouts. Delays are particularly troublesome in deep drilling operations where the drill bit may be 5,000 feet to 15,000 feet below the surface. In these conditions the time lag between influx and detection at the surface might exceed two hours. Accordingly, it would be highly advantageous to be able to determine influx near the drill bit and immediately to telemeter this desired information to the surface.
In recent years, a number of systems have been developed that have been designed to detect more rapidly the influx of external fluids into a well borehole during drilling of the well borehole These methods have employed sensors mounted on or near the drill bit so that the sensors measure the influx of external fluids soon after the drill bit enters a geological formation containing formation fluids under high pressure which migrate into the drilling fluid. Any conventional borehole telemetry system may then be used for transmitting the acquired data to the surface for immediate analysis. The preferred systems now appear to comprise the various mud pulse telemetry systems, including positive, negative and acoustic telemetry systems, which telemeter the information to the surface at the speed of sound.
Several apparatus and methods for determining influx near the drill bit and telemetering that information to the surface have been disclosed. U.S. Pat. No. 4,492,865 discloses an apparatus and method for determining influx in a borehole using gamma radiation to measure the density of the fluid in the borehole U.S. Pat. No. 3,776,032 discloses an apparatus and method for detecting influx employing acoustic waves to measure gas influx and resistivity to measure water influx.
Other methods of determining downhole characteristics of the geological formation or of the well bore fluids are well known to those skilled in the art. However, those characteristics have not been measured and used to determine influx. For example, U.S. Pat. No. 4,571,693 discloses an apparatus and method for determining density of the fluid using acoustic, preferably ultrasonic, waves. U.S. Pat. No. 4,536,713 discloses an apparatus and method for determining resistivity of a flowing drilling fluid using eddy currents generated in the fluid in a gap in a ferrite core encircled by a magnetic coil to which a constant current or voltage has been applied. However, none of these methods have been employed to determine influx of formation fluids into the drilling fluid in the annulus surrounding the drill string.
Other systems have been used to determine electrical characteristics of the surrounding geological formation. In fact, geological formations have been electrically logged for more than half a century. U.S. Pat. No. 4,360,778 discloses the high frequency induction logging of a geological formation to locate interfaces between different zones in the formation. U.S. Pat. No. 4,009,434 discloses dielectric well logging for determining water and residual oil saturation in the surrounding geological formation. A multitude of patents have been directed to the determination of the dielectric constant or the resistivity of the surrounding formation. For example, U.S. Pat. Nos. 4,626,785; 4,278,941; and 4,319,191 all disclose apparatus and methods for determining the dielectric constant of the formation surrounding the borehole. U.S. Pat. Nos. 4,012,689; 3,891,916; 3,982,176; and 3,993,944 all disclose apparatus and methods for determining not only the dielectric constant, but also resistivity of the formation surrounding the borehole. However, none of these techniques have been employed to determine the dielectric constant or conductivity of the fluid in the borehole or to determine influx therefrom.
The prior art systems described above fail to provide an ideal influx detection system. Those skilled in the art still desire a simple, efficient, accurate and timely influx detection system. Accordingly, there has been a long felt but unfulfilled need within the oil and gas drilling industry for a system, apparatus and method for efficiently, accurately and quickly determining influx at or near the drill bit and telemetering that information to the surface where it is immediately available for use by the drilling operator